The present invention relates to electric clothes pressing irons having a soleplate composed of a metal sheet possibly bent up at its edges and having a lower face that constitutes, with the exterior of the edges, the working face in contact with the articles to be ironed when the iron is in its ironing position. Generally, such iron further include a heating body associated with the soleplate, the heating body most often being made of aluminum and including the heating element of the iron.
Soleplates of pressing irons desirably have an attractive appearance, and must have a good resistance to corrosion, good sliding properties with respect to fabrics to be ironed, and a surface hardness which causes them to resist scratching. Resistance to scratching is necessary to maintain the sliding qualities and to resist adverse effects of inappropriate uses, such as for example a passage of the iron over a zipper.
For this purpose, numerous surface treatments have already been proposed. For example, it is known to cover soleplates of aluminum or steel with an enamel coating. It is also known to coat the soleplate surface with a ceramic by plasma spraying as in the European patent document EP 227111, or by any other procedure such as, for example, by anodization as described in the French patent document FR 2717833. It has also been proposed to perform chemical surface treatments, such as a treatment with phosphates which improves corrosion resistance and aids sliding. It is also known to coat the soleplate with a product such as polytetrafluoroethylene.
The European patent document EP 726351 describes a process that is particularly adapted to aluminum soleplates, in which both surfaces are treated by xe2x80x9cshot peeningxe2x80x9d, which is a treatment in which the surfaces are subjected to a jet of particles driven in an air jet, for the sole purpose of improving the flatness, or planarity, of the surface. To achieve the desired result, both surfaces must be treated simultaneously and symmetrically.
These treatments are particularly useful on soft surfaces, such as aluminum surfaces, or steel surfaces to also protect them from corrosion. French patent document FR 2567929 discloses an aluminum surface reinforced by a stainless steel plate. The stainless steel surfaces do not corrode easily, have an attractive appearance, which can be provided by a shiny finish, and have acceptable sliding properties. Most often they can be used without a surface treatment, other than a possible finishing polish.
However, stainless steel, although more resistant to scratching, remains all the same subject to scratching, and the finish can be deteriorated, which requires that the soleplates be protected at the point of sale by a plastic film. In addition, it is desirable to improve the coefficient of sliding friction of the soleplate on the fabric to be ironed.
The present invention provides a clothes pressing iron having a metal soleplate with a working surface of steel, preferably of stainless steel, having an improved coefficient of friction and an improved hardness to improve the resistance to scratching and to improve the ease with which the soleplate slides on the fabric.
Primarily, the invention provides a metal soleplate for a pressing iron in which the working surface of the soleplate is composed of crystalline grains that are deformed by compression perpendicular to the surface, the number of metal grain dislocations per unit of volume being at least 40% greater than that of the metal at the interior of the soleplate. For this purpose, only the lower surface of the soleplate, which is the surface that will contact the articles being ironed, need be subjected to such deformation.
Metal dislocations are understood to be discontinuities in the crystalline metal structure, whether these are between metal grains or constituted by defects, or discontinuities, within the grains.
The interior of the soleplate is here defined as a region of the metal that is remote from the surfaces, to a depth greater than 40 xcexcm.
The compression of the surface causes it to be smoothed, reduces the coefficient of friction of the surface on the fabric to be ironed and closes pores which might be preexisting. The compression also increases the hardness and creates internal stresses that enable the exterior surface to resist damage.
Preferably, the thickness of the compressed part of the metal, measured from the surface, is between 25 and 35 xcexcm.
This thickness varies according to the control of the mode of producing the compression. It is preferred to select a compromise between a high level of hardness, which necessitates a compression to a great depth but where a correct surface state is difficult to obtain, and a good surface state, which promotes sliding.
Preferably, the soleplate is made of stainless steel and has at its working surface a Vickers hardness at least 25% greater than the Vickers hardness measured at the interior of the soleplate.
The hardness at the interior of the soleplate is that which exists in a metal zone situated at a depth of the metal soleplate beyond the compressed region. It is equal to the hardness of the metal before the compression treatment.
For example, the surface of a stainless steel plate having a Vickers hardness of less than 400 at the interior has a Vickers hardness greater than 500 at the surface, or a minimum increase in hardness of 25%.
Preferably, the roughness of the working surface, measured according to the standard DIN 4777, is less than 3 xcexcm.
One thus obtains a metal soleplate having a good resistance to scratching and a good slidability on the fabric.
Preferably, compression of the surface of the stainless steel is obtained by a xe2x80x9cshot peeningxe2x80x9d process.
This process includes the projection of essentially nonabrasive particles onto the soleplate surface by entraining the particles in a jet of expanded air, the air being, prior to expansion, placed at a pressure of the order of 2 bars. Hammering of the surface by the particles produces the desired compression of the metal grains of the stainless steel. The cloud of particles produces a very regular effect and is much easier to control than does compression by rolling, for example. This process is applied equally to the edges of the soleplate in a more convenient manner than other mechanical processes.
Preferably, the treatment of the surface by shot peening is effectuated in a single operation.
In particular there is no preliminary abrasion, or thermal treatment of the stainless steel. The projection, or spraying, is performed at normal room temperature. This permits a less costly treatment.
Preferably, the particles utilized are a mixture of glass beads, ceramic beads and natural granular materials.
This mixture permits controlling the hammering of the surface by producing different impacts that result in a smoothing of the surface as well as a deformation to a certain depth below the surface.